From our roots outward, we Osteospermum require a specific balance of nutrients to thrive, not just survive. Our primary needs are captured in the NPK ratio on fertilizer packages. Nitrogen (N) is crucial for our vigorous leafy growth and the development of our deep green foliage, which is the engine of our photosynthesis. However, too much nitrogen can make us leggy and reduce our most prized feature: our profuse blooms. Phosphorus (P) is essential for strong root development and, most importantly, for energy transfer within our systems to support prolific flowering and robust seed production. Potassium (K) is the regulator; it ensures our overall cellular functions, water uptake, and disease resistance are operating smoothly, making us sturdier plants.
For us, a balanced or slightly bloom-boosting fertilizer is ideal. A formula with equal parts, like a 10-10-10 or 14-14-14, provides a solid foundation for all-around health. However, to truly encourage the spectacular floral display gardeners love, a formula where the phosphorus (the middle number) is slightly higher can be beneficial—something like a 5-10-5 or a 12-15-12. We strongly advise against high-nitrogen fertilizers (where the first number is disproportionately large, e.g., 24-6-6), as this will direct our energy into leaves at the expense of your desired flowers.
Our feeding needs change with the seasons. At planting time, if you amend the soil with a generous amount of compost or a slow-release granular fertilizer, that will provide us with a steady, gentle supply of nutrients as we establish our roots. Once we are established and begin to set buds (typically in late spring), a regular but light feeding regimen should begin. A monthly application of a water-soluble fertilizer, diluted to half the recommended strength, is perfect. This consistent, gentle feeding supports continuous blooming without the risk of fertilizer burn, which can shock our systems. As the days shorten and temperatures cool in late autumn, our growth naturally slows. Please cease fertilization then to allow us to harden off and prepare for dormancy or a period of rest.
The method of application is as important as the formula itself. Always ensure our soil is moist before applying any fertilizer; applying to dry soil can damage our delicate root hairs. For granular, slow-release fertilizers, work them gently into the soil around our base at the beginning of the season, being careful not to concentrate them directly against our main stem. For liquid fertilizers, the best practice is to apply the diluted solution directly to the soil, not over our leaves (foliar feeding), to avoid potential leaf burn and to ensure the nutrients go directly to our roots where they are absorbed most efficiently. A thorough watering after application helps move the nutrients into the root zone.
